1. Field of the Invention
The present invention generally relates to planar antennas, and more particularly to multilayer planar antennas having small dimensions and in the industrial, scientific and medical (ISM) band with an omnidirectional pattern in the horizontal plane.
2. Description of the Related Art
The ISM band is currently being used for many medium data rate devices such as local area networks (LANs). Adaptor cards are currently being designed in a Personal Computer Memory Card International Association (PCMCIA) form factor for remote "laptop" computers. These local area networks (LANs) adaptor cards benefit from an elimination of the cabling usually associated wired adaptor cards. They enable one to connect to "backbone" networks such as "Ethernet" and token ring networks.
For wireless products, such as wireless local area network (LAN) adapters, an omnidirectional pattern is desired in the horizontal plane because most adaptors are oriented such that communication between adaptors occurs in this plane. For purposes of this application, the horizontal plane is defined as the plane containing the antenna. Furthermore, the peak power should be in the horizontal plane because this results in the largest maximum distance at which the adaptors would function.
If the LAN has a Personal Computer Memory Card International Association (PCMCIA) form factor, the antenna must have dimensions smaller than 4 cm.times.5.4 cm for a type II card. Furthermore, the recommended bump should not exceed 10.5 mm in height so that the antenna in the device packaging can be outwardly concealed. For purposes of this application, the "bump" is the height of the extension of the antenna.
Additionally, if the radio uses a spread spectrum approach, as is known in the art, the 84 MHz bandwidth requirement from 2.4 GHz-2.483 GHz in the ISM band must be met by the antenna because the radio utilizes frequencies in this range.
Hitherto the invention, the pattern, form factor and bandwidth restrictions were very difficult to simultaneously meet and no conventional antenna was known which optimized each of these restrictions.